Flexible printed circuits and rigid-flexible printed circuits are used in many applications where at least certain parts of the circuits need to be installed in a curved or bent state. Flexible printed circuits incorporate metal lines sandwiched between non-conductive flexible layers of flexible printed circuit. However, as more layers of metal and non-conductive substrates are added to the sandwich, the flexible printed circuit becomes less flexible. In addition, attempts to add electrical or electronic devices require the mounting of components onto the surfaces of the flexible circuit. The surface mounted components, i.e., surface mounted devices (SMDs), make the flexible circuit assembly even more rigid and less flexible, and substantially increase the height of the flexible circuit assembly. Technologies exist to include components inside thick, rigid glass-reinforced epoxy printed circuit boards, such as FR4, components are conventionally still mounted onto surfaces of FR4 boards and not embedded inside. Issues such as the complexity of inclusion process, high mechanical stresses, poor yield, poor thermal management, and high cost prevented inclusions of components inside FR4 for products.
Electronic systems are often partitioned onto two or three circuit boards. Rigid printed circuit boards (FR4 PCBs) are used to mount and support the electronic devices and include many copper layers to interconnect the respective SMDs. Separate flexible interconnects are used to provide interconnection between the individual rigid PCBs. Also, the flexible circuits are typically structured with two or more metal layers. Thus, the system is somewhat flexible in the interconnect flex circuit regions, but rigid where components are mounted. Bendable regions of a flex circuit generally do not contain surface mounted component because of bending stresses could be exerted on solder joints that could lead to disruptions of electrical paths. Today's multi-component system is not optimized for size and weight parameters. Furthermore, the combined PCB—flex manufacturing process is complex and expensive. Designs for flat heat sinks and bendable heat sinks are complex and limited. Rigid flex technology employs methods to thicken and stiffen a region of the flexible circuit to provide a region that is mechanically rigid to accommodate fragile components, e.g., surface mount devices and through-hole connectors. The process for inclusion of SMDs is likewise complex and less cost effective. For example, over-molding of devices such as semiconductor circuits, requires additional packaging and assembly processes. Discrete devices that are diced from a wafer to form a die are first assembled into a packaged device, and the packaged device is then mounted to a PCB to complete assembly.
In addition, the aforementioned PCB substrates are poor conductors of heat. Therefore, when heat generated by the mounted device is excessive, e.g., in the case of power circuits, microprocessors, and light-emitting devices, more expensive thermally conductive substrates accompanied with the attachment of a bulky conducting heat sink are required. The heat sink is attached to the underside of a metal core substrate, FR4 PCB, or on top of the packaged SMD to transfer heat away from the mounted device. Waste heat passes only slowly through insulating packaging materials and through circuit boards. The heat sink is typically metallic copper or aluminum and its attachment to the substrate or package makes the assembly bulky, heavy, and inflexible. Also, shielding of electronics from electromagnetic interference (EMI) conventionally require additional metal casings around FR4 PCB.
Therefore, despite all the existing flexible, rigid and FR4 PCB technologies, in light of the above deficiencies of the background technology, what is needed is an adaptable, bendable and cost-effective method of manufacturing flexible circuit assemblies that permits mounting of an increased number of devices in a cost effective weight and space saving manner, transfers heat efficiently away from heat generating devices, protect against EMI, and allows the use of highly effectual automated roll-to-roll manufacturing concepts.